As shown in the U.S. patent to W. G. H. Finch, U.S. Pat. No. 2,422,788, it is known in the art of facsimile transmission ot employ a prism to generte a color-dispersed band of light from a polychromatic point illuminating source and to use focused portions of the band of light to sequentially scan successive lines of a source document; first by illuminating a document with a spot of one color and subsequently by illuminating with spots of two additional colors. For such an imaging system, a photo-electric cell, responsive to light impulses over the entire spectrum, is employed to generate an electrical signal that is proportional to the intensity of the scanning light. Thus, separate electrical signals corresponding to the separate color components of the lines of the source document are generated.
However, such a prior art facsimile transmission apparatus necessarily requires a plurality of scans of each line of a source document and, therefore, is rather slow in operation. Also, the moving prism further reduces the speed, efficiency and reliability of the apparatus.
It is also known in the color facsimile transmission art to employ red, green and blue filters to produce color component images of a corresponding incident polychromatic primary image. In such systems, the component images are applied to irradiate corresponding photodetectors that generate electrical signals that are proportional to the intensity of the light of each of the images. It has also been suggested to vary the size of such color filters in order to compensate for the sensitivity of the photodetectors to particular wavelengths of light. However, such prior art filter imaging systems necessarily require a relatively intense polychromatic primary image. Also, such systems waste a relatively large amount of the radiation intensity of the polychromatic image by filtering out unwanted color components.
It is known to use charge coupled devices (CCDs) to generate packets of charge that correspond to picture elements (pixels) of an incident light image.
For color imaging, it is also known to employ three CCD arrays to provide electrical signals corresponding to the intensities of the red, green and blue color components of a polychromatic image. For example, such CCD imaging apparatus is disclosed in the patent to Morishita et al, U.S. Pat. No. 4,007,488.
In the patent to Morishita it is suggested that the charge accumulation time of a frame transfer imaging CCD may be adjusted in inverse relation to the sensitivity of the CCD to the wavelength of incident light. Thus, the electrical output of each adjusted CCD is a function of the intensity of the incident light and not the wavelength of the light. However, the apparatus of Morishita requires relatively expensive beam splitters and other optical components to apply a separate filtered image to each of the CCDs. In addition, the optical apparatus of Morishita requires rather precise alignment.
It is known in the CCD imaging art to operate a CCD array of imaging elements in a time delay and integration (TDI) mode. For example, the publication, David F. Barbe, "Imaging Devices Using the Charge Coupled Concept", Proc. IEEE, Vol. 63, pp. 38-67 (January, 1975) describes a TDI system. In the TDI mode, an incident light image is scanned across rows of cells of the parallel registers of a particular CCD array and the parallel registers of the array are synchronously gated so that a plurality of charge packets corresponding to the pixels of the image accumulate under the image as the image moves over the parallel registers. After the image has moved the length of the parallel registers of the CCD array, the accumulated charges are passed to a serial register and are thereafter gated from the serial register.
Although the TDI operation of CCDs is known to the art, CCDs have not heretofore been operated in the TDI mode to provide electrical signals corresponding to the color components of a polychromatic image.
Accordingly, it is a primary object of the invention to provide a relatively simple and inexpensive imaging apparatus that uses a plurality of CCD arrays operated in a time delay and integration mode to generate signals corresponding to the pixels of optical components of a primary image.
Another object of the invention is to provide such an apparatus wherein the number of cells in the parallel registers of the imaging CCD arrays are varied to compensate for the sensitivity of each CCD to a particular wavelength of incident light.
A further object of the invention is to provide a simple, reliable and less expensive color facsimile transmission apparatus that employs a prism or grating to irradiate a source document with a band of color-dispersed illumination which is then imaged onto a plurality of photosensitive CCDs.
Another object of the invention is to provide an easily aligned imaging apparatus by using a plurality of pre-aligned arrays that are formed on a single chip or mounted on a substrate.